Submission #233409

#	Time	Username	Problem	Language	Result	Execution time	Memory
233409		dolphingarlic	Islands (IOI08_islands)	C++14	48 / 100	608 ms	131072 KiB

islands

#include <bits/stdc++.h>
#define FOR(i, x, y) for (int i = x; i < y; i++)
typedef long long ll;
using namespace std;

vector<pair<int, ll>> graph[1000001], stck, cycle;
ll discarded, ans = 0, cmp_ans, dp[1000001], p[5][1000001];
bool processed[1000001], on_stck[1000001], on_cycle[1000001];

bool find_cycle(int node, pair<int, ll> parent = {0, 0}) {
    on_stck[node] = true;
    for (pair<int, ll> i : graph[node]) if (i != parent) {
        stck.push_back({node, i.second});
        if (on_stck[i.first]) {
            cycle.push_back({i.first, 0});
            on_cycle[i.first] = true;
            while (stck.back().first != i.first) {
                cycle.push_back(stck.back());
                on_cycle[stck.back().first] = true;
                stck.pop_back();
            }
            discarded = stck.back().second;
            return true;
        }
        if (find_cycle(i.first, {node, i.second})) return true;
        stck.pop_back();
        on_stck[i.first] = false;
    }
    return false;
}

void calc_tree(int node, int parent = 0) {
    processed[node] = true;
    ll mx = 0, sc = 0;
    for (pair<int, ll> i : graph[node]) if (i.first != parent && !on_cycle[i.first]) {
        calc_tree(i.first, node);
        if (dp[i.first] + i.second > mx) sc = mx, mx = dp[i.first] + i.second;
        else if (dp[i.first] + i.second > sc) sc = dp[i.first] + i.second;
    }
    dp[node] = mx;
    cmp_ans = max(cmp_ans, mx + sc);
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    FOR(i, 1, n + 1) {
        int v;
        ll l;
        cin >> v >> l;
        graph[i].push_back({v, l});
        graph[v].push_back({i, l});
    }

    FOR(i, 1, n + 1) if (!processed[i]) {
        stck.clear(); cycle.clear();
        find_cycle(i);

        cmp_ans = 0;
        int m = cycle.size();

        FOR(j, 1, m) p[0][j] = p[0][j - 1] + cycle[j].second;
        for (int j = m - 2; ~j; j--) p[1][j] = p[1][j + 1] + cycle[j + 1].second;

        FOR(j, 0, m) {
            calc_tree(cycle[j].first);
            p[2][j] = dp[cycle[j].first] - p[0][j];
            p[3][j] = dp[cycle[j].first] + p[0][j];
            p[4][j] = dp[cycle[j].first] + p[1][j];
        }

        ll mx = p[2][0];
        FOR(j, 1, m) {
            cmp_ans = max(cmp_ans, p[3][j] + mx);
            mx = max(mx, p[2][j]);
        }
        mx = p[4][m - 1];
        for (int j = m - 2; ~j; j--) {
            cmp_ans = max(cmp_ans, p[3][j] + mx + discarded);
            mx = max(mx, p[4][j]);
        }

        ans += cmp_ans;

        FOR(j, 0, 5) FOR(k, 0, m) p[j][k] = 0;
    }
    cout << ans;
    return 0;
}

• Subtask 1: 15 / 33
• Subtask 2: 3 / 3
• Subtask 3: 0 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10